The objectives of this project are to: 1) Elucidate the role of conformational changes, segmental flexibility, and domain interactions in the molecular mechanism of effector activation in IgM and IgG antibodies, and 2) to determine the antigenic specificity of a new murine IgM myeloma protein produced by ABPC 22. These problems will be investigated primarily by means of nanosecond fluorescence, circular dichroism, and perturbed angular correlation techniques. Our specific aims for the project period are to: 1) Determine the role of the C mu 2 domains of IgM in the transfer of information from the antibody combining site in Fab to the complement binding site in Fc; 2) to determine the biological effects of segmental flexibility in IgG by measurement of any changes in flexibility caused by hapten binding at the active site; 3) to measure the binding properties of ABPC 22 IgM myeloma protein with dansyl conjugated proteins and search for a more "natural" antigen.